Negative pressure device

ABSTRACT

A method and apparatus are disclosed for providing negative pressure at a wound site. The apparatus includes a suction pump for generating negative pressure, a negative pressure reservoir, a valve element arranged to selectively provide a fluid communication path between the reservoir and the wound site while a negative pressure in the negative pressure reservoir is greater than a threshold negative pressure, to thereby provide a desired negative pressure at the wound site, and wherein in response to a pressure in the negative pressure reservoir decreasing to the threshold negative pressure, the suction pump is operable to re-establish an initial negative pressure in the negative pressure reservoir.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase of PCT InternationalApplication No. PCT/GB2011/051748, filed on Sep. 16, 2011, designatingthe United States and published on Mar. 29, 2012 as WO 2012/038727,which claims priority to Great Britain Patent Application No. 1015710.5,filed on Sep. 20, 2010 and to Great Britain Patent Application No.1015709.7, filed on Sep. 20, 2010. The disclosure of all three of theabove-referenced applications are incorporated by reference herein intheir entireties and should be considered a part of this application.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present invention relates to an apparatus and method for providingnegative pressure at a wound site. In particular, but not exclusively,the present invention relates to an apparatus including a negativepressure reservoir able to continually or repeatedly “top up” an appliednegative pressure so that negative pressure applied at a wound site canbe maintained within desired limits for a relatively long period of timewithout operation of a powered source of negative pressure. The presentinvention also relates to an apparatus and method for selectivelyproviding a fluid communication path. In particular, but notexclusively, the present invention relates to an apparatus forconnecting two chambers containing negative pressures and capable ofregulating the communication of negative pressure between the twochambers.

Background

Devices for the generation of negative pressure at the surface of skinhave been used for many hundreds of years to treat animal and humanbodies. For example the cupping technique (which relates to thepositioning of a mouth of a rigid vessel containing hot air) is a wellknown technique. Spring powered syringes and suction cups are othermechanical techniques which have been used in the past for generating avacuum on tissue. In common with cupping such techniques have, in thepast, suffered from a very limited longevity of the therapy which can beapplied. That is to say the duration of the negative pressure which canbe maintained over a site of application has been limited.

To enable a more prolonged application of controlled negative pressure,powered systems, which include a vacuum generation source such as a pumpof some type, have been developed and many examples of such systems areused today for the management of wounds. However, many of these systemsare not convenient for discreet use by a patient as they are large, canbe heavy and are often noisy.

Furthermore, such systems rely on continuous connection of the patientto the vacuum generation source. Disconnection from the vacuumgeneration source may be possible for short periods, but such periodsshould be minimized as prolonged disconnection can increase the risk ofdressing failure and of ingress of contaminants into the wound(including bacteria).

Some patients having relatively less severe wounds which do not requirecontinuous hospitalisation, for example, but whom nevertheless wouldbenefit from the prolonged application of TNP therapy, could be treatedat home or at work subject to the availability of an easily portable andmaintainable TNP therapy apparatus. To this end GB-A-2 307 180, which isherein incorporated by reference, describes a portable TNP therapy unitwhich may be carried by a patient and clipped to belt or harness. Anegative pressure can thus be applied at a wound site. However, thedescribed portable TNP apparatus still relies on a continuous connectionof the wound site to a powered vacuum source to provide the negativepressure at the wound site.

In order to maintain the negative pressure at the wound site, the vacuumgenerator, commonly a pump, operates at a frequency dictated by fluid(exudate or gas) ingress into the system during its operation. Fluidingress rates may be at a level that results in the pump runningunpredictably every few minutes or tens of minutes. The powered vacuumsource, or pump, creates noise, vibration and heat.

The intermittent operation of a pump and its associated valving createsa level of noise and vibration that is difficult to perceive in aworking environment (office, hospital) but becomes all too obvious inthe home, particularly when attempting to sleep. Noise levels in workingenvironments (including air conditioning units and other electronicequipment) are frequently above 50 dB while those in the home, duringthe night, are frequently less than 20 dB.

The noise and vibration levels created by the unpredictable andintermittent operation of the powered pump in current NPWT systems isfrequently unacceptable for home use and negatively impacts quality oflife of the patient.

Pressure regulators can be used to control the communication of pressurebetween an inlet and an outlet, in order to provide a desired stablepressure level. For example, there exist certain medical applications inwhich it is desirable to apply a negative pressure to a body location,however the level of negative pressure provided by a vacuum pump may beexcessive and a regulator may be used to control the negative pressurecommunicated to the application site.

In International Patent Application, WO 96/11031, a method and apparatusfor draining a closed wound employing sub-atmospheric pressure isdescribed. A regulator valve is described that is able to regulate theapplied sub-atmospheric, or negative pressure, to the closed wound. Theregulator valve is controllable to allow a desired negative pressure tobe set by a user.

When used for medical applications, the regulator cannot be reused dueto the possibility of contamination by the drained wound fluids, andtherefore must be single use. Current regulator valves such as thatdescribed in WO 96/11031 are relatively complex and therefore the costof disposing of the regulator after a single use can be significant.

SUMMARY OF SOME EXEMPLIFYING EMBODIMENTS

It is an aim of the present invention to at least partly mitigate theabove-mentioned problems.

It is an aim of certain embodiments of the present invention to providean apparatus which can provide a negative pressure at a wound site foran extended period without requiring the operation of a powered sourceof negative pressure. This enables a user to sleep undisturbed.

It is an aim of certain embodiments of the present invention to providea system for decoupling the operation of a powered source of negativepressure from a level of hysteresis specified for a wound site.

It is an aim of certain embodiments of the present invention to providean apparatus for reliably regulating the communication of negativepressure between an inlet and an outlet that has a simple constructionand is of reduced cost.

According to the present invention, there is provided apparatus forproviding negative pressure at a wound site, comprising:

-   -   a suction pump for generating negative pressure;    -   a negative pressure reservoir;    -   a valve element arranged to selectively provide a fluid        communication path between the reservoir and the wound site        while a negative pressure in the negative pressure reservoir is        greater than a threshold negative pressure, to thereby provide a        desired negative pressure at the wound site; and wherein    -   in response to a pressure in the negative pressure reservoir        decreasing to the threshold negative pressure, the suction pump        is operable to re-establish an initial negative pressure in the        negative pressure reservoir.

According to the present invention, there is provided a method ofproviding negative pressure at a wound site, comprising the steps of:

-   -   while a negative pressure in a negative pressure reservoir is        greater than a threshold negative pressure, selectively        providing a fluid communication path between the negative        pressure reservoir and the wound site via a valve element to        provide a desired negative pressure at the wound site; and    -   in response to the negative pressure in the negative pressure        reservoir decreasing to the threshold negative pressure,        re-establishing the initial negative pressure in the negative        pressure reservoir via a suction pump.

According to the present invention, there is provided a method oflimiting runtime of a suction pump for providing negative pressure at awound site, the method comprising:

-   -   via the suction pump, providing an initial negative pressure in        a negative pressure reservoir;    -   selectively providing a fluid communication path between the        reservoir and the wound site to provide a desired negative        pressure at the wound site; wherein    -   the suction pump is only run when a negative pressure in the        negative pressure reservoir is depleted to a threshold negative        pressure.

According to the present invention, there is provided apparatus forselectively providing a fluid communication path comprising:

-   -   a channel element comprising opposed sidewall elements locatable        in an open spaced apart configuration in which a channel is        provided between the sidewall elements and in a closed        configuration in which the sidewall elements abut to close the        channel; wherein    -   the sidewall elements are resilient and are moveable to said        open configuration in which the channel provides a fluid        communication path or said closed configuration responsive to a        pressure difference at the sidewall elements.

According to the present invention, there is provided a method ofselectively providing a fluid communication path between first andsecond zones of negative pressure, the method comprising:

-   -   coupling a channel element between a first zone of negative        pressure and a second zone of negative pressure, wherein the        channel element comprises opposed sidewall elements locatable in        an open spaced apart configuration and in a closed configuration        wherein the sidewall elements abut to close the channel, wherein        the sidewall elements are resilient; and    -   via a pressure difference acting on the resilient sidewall        elements, moving the resilient sidewall elements between said        open configuration in which the channel provides a fluid        communication path between the first and second zones of        negative pressure and said closed configuration responsive to        the pressure difference.

According to of the present invention, there is provided a method ofmanufacturing a channel element for selectively providing a fluidcommunication path, the method comprising:

-   -   overlying a masking strip on a first surface of a first sidewall        element, the masking strip defining a channel region;    -   forming a second sidewall element overlying the first surface of        the first sidewall element and the masking strip such that in        areas of the first surface where the masking strip is absent the        first and second sidewall elements are bonded together; and    -   removing the masking strip from in-between the first and second        sidewall elements, said first and second sidewall elements        comprising said channel element.

According to another aspect of the present invention, a method oflimiting runtime of a suction pump for providing negative pressure at awound site is provided, the method comprising:

-   -   via the suction pump, providing an initial negative pressure in        a negative pressure reservoir; and    -   selectively providing a fluid communication path between the        reservoir and the wound site to provide a desired negative        pressure at the wound site,    -   wherein the suction pump is only run when the negative pressure        in the negative pressure reservoir is depleted to a first        threshold negative pressure; and    -   wherein selectively providing the fluid communication path        comprises:        -   coupling a channel element between a first zone of negative            pressure and a second zone of negative pressure, wherein the            channel element comprises opposed sidewall elements            locatable in an open spaced apart configuration and in a            closed configuration wherein the sidewall elements abut to            close the channel, wherein the sidewall elements are            resilient; and        -   via a pressure difference acting on the resilient sidewall            elements, moving the resilient sidewall elements between            said open configuration in which the channel provides a            fluid communication path between the first and second zones            of negative pressure and said closed configuration            responsive to the pressure difference.

According to another aspect of the present invention, a method ofproviding negative pressure at a wound site is provided, the methodcomprising:

-   -   while a negative pressure in a negative pressure reservoir is        greater than a first threshold negative pressure, selectively        providing a fluid communication path between the negative        pressure reservoir and the wound site via a valve element to        provide a desired negative pressure at the wound site; and    -   in response to the negative pressure in the negative pressure        reservoir decreasing to the first threshold negative pressure,        re-establishing the initial negative pressure in the negative        pressure reservoir via a suction pump,    -   wherein selectively providing the fluid communication path        comprises:        -   coupling the valve element between a first zone of negative            pressure and a second zone of negative pressure, wherein the            valve element comprises opposed sidewall elements locatable            in an open spaced apart configuration and in a closed            configuration wherein the sidewall elements abut to close            the channel, wherein the sidewall elements are resilient;            and        -   via a pressure difference acting on the resilient sidewall            elements, moving the resilient sidewall elements between            said open configuration in which the channel provides a            fluid communication path between the first and second zones            of negative pressure and said closed configuration            responsive to the pressure difference.

In some embodiments, the methods further comprise:

-   -   placing a wound dressing over a wound or wound site, the wound        dressing forming a substantially fluid tight seal over the wound        or wound site; and    -   connecting the negative pressure reservoir to the wound        dressing.

In some embodiments, providing the desired negative pressure at thewound site from the negative pressure reservoir is accomplished withoutrequiring the operation of a powered source of negative pressure,activating the suction pump, activating a motor, causing a membrane ordiaphragm to move, or the like.

In some embodiments, moving the resilient sidewall elements furthercomprises moving the resilient sidewall elements between a partiallyopen configuration and a closed configuration.

In some embodiments, providing the pressure difference comprises:

-   -   applying a negative pressure at the second zone of negative        pressure to be communicated to the first zone of negative        pressure via the channel or valve element, wherein the negative        pressure in the second zone of negative pressure is greater than        the negative pressure in the first zone of negative pressure;        and    -   wherein the sidewall elements are urged together to close the        fluid communication path if the negative pressures in the first        and second zones of negative pressure are greater than a second        threshold pressure.

In some embodiments, the first zone of negative pressure comprises thewound site and the second zone of negative pressure comprises thenegative pressure reservoir.

In some embodiments, the first zone of negative pressure comprises thenegative pressure reservoir and the second zone of negative pressurecomprises the wound site.

Certain embodiments of the present invention enable the decoupling ofnarrow hysteresis limits from the operation of a powered source ofnegative pressure when applying negative pressure at a wound site. Thus,the applied negative pressure can be maintained within narrow hysteresislimits without requiring constant or very frequent operation of a pump.

Certain embodiments of the present invention provide the advantage ofallowing negative pressure applied to a wound site to be maintainedwithin hysteresis limits for a prolonged silent period in which apowered source of negative pressure is not operated.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the present invention provide the advantage of asimple and cheap disposable valve element that can be used to regulatethe communication of negative pressure according to a design thresholdpressure.

Embodiments of the present invention will now be described hereinafter,by way of example only, with reference to the accompanying drawings inwhich:

FIG. 1 illustrates a prior art arrangement for applying negativepressure to a wound site;

FIG. 2 illustrates an arrangement including a vacuum reservoir forapplying negative pressure to a wound site; and

FIG. 3 illustrates negative pressure levels during operation of thearrangement of FIG. 2.

FIG. 4 illustrates a valve element;

FIG. 5 illustrates cross-sections through a valve element duringoperation;

FIG. 6 illustrates a graph of operating pressures in two chambersconnected via a valve element;

FIG. 7 illustrates a method of manufacturing a channel element;

FIG. 8 illustrates assembly of a valve element;

FIG. 9 illustrates cross-sections through a valve element havingdifferent mounting spacings; and

FIG. 10 illustrates an arrangement for applying negative pressure to awound site including a valve element.

FIGS. 11 and 12 illustrate the manufacturing process of a deformabletube valve in which FIG. 11 illustrates the tube before deformation.

FIG. 13 illustrates an alternative manufacturing process for adeflatable tube valve.

FIGS. 14, 15, 16, 17 and 18 illustrate the manufacture of a specificembodiment of the deformed tube valve.

In the drawings like reference numerals refer to like parts.

DETAILED DESCRIPTION OF SOME EXEMPLIFYING EMBODIMENTS

FIG. 1 illustrates a prior art arrangement for applying negativepressure wound therapy to a wound site 10. A packing material 12 isplaced within a wound cavity, and then a drape 14 sealed to the surfaceof the skin around the wound site 10 forming a fluid tight seal aroundthe perimeter of a wound chamber. A source of negative pressure, such asa pump 20 is coupled to the wound cavity via a tube 16. A fluidcollection canister 18 is coupled between the pump 20 and the woundchamber to collect any wound exudate drawn from the wound site 10. Theuse of the packing material 12 such as a foam, gauze or the like isoptional, and it may be omitted in certain arrangements as appropriate.

Also whilst embodiments of the present invention will be describedhereinafter by way of reference to a wound chamber defined at a woundsite under a drape it will be understood that certain embodiments of thepresent invention can be utilised to maintain a negative pressure in awound chamber which is a rigid structure or partly rigid structure suchas a cup device placed over a wound site.

In operation, the pump 20 operates to generate a negative pressure inthe fluid collection canister 18 and the wound chamber to thereby applya desired negative pressure to the wound site 10. Over time, smallleakage paths will form that allow fluid to leak into the wound chamber.Ingress of fluid such as wound exudate or gas (such as air from theenvironment) into the wound chamber will lead to the negative pressureat the wound site slowly degrading, i.e. the pressure becoming lessnegative. Once the pressure degrades to a certain level, the pump 20operates to re-establish the desired negative pressure at the wound site10.

The quiet period between pump-operations is defined by both fluidingress rate and a level of vacuum hysteresis specified by the pumpcontrol system. It will be understood by the skilled man that a controlsystem running with 10% hysteresis means that a system initially attainsa vacuum level V and this level decays to 90% of its original levelbefore being replenished by the vacuum source. Quiet periods areprolonged in direct proportion to the percentage of hysteresis that istolerable in the system. A system with 100% hysteresis will bereplenished 100-times less frequently than a system with 1% hysteresis.Commonly, in current systems, hysteresis is minimized to below 10% ofthe target vacuum level because it is believed that this specificity istherapeutic.

Thus, in the arrangement of FIG. 1, the pump 20 operates to re-establishthe desired negative pressure depending on the hysteresis level definedfor the system. This leads to regular operation of the pump to maintainthe desired negative pressure at the wound site 10.

The pump to produce the high vacuum reservoir may be a mechanical ormanual pump. The advantage of using a high vacuum reservoir is that theperiod between top ups of negative pressure is increased, thus reducingthe inconvenience to the user.

According to embodiments of the present invention as discussed furtherbelow, the operation of a pump to provide negative pressure is decoupledfrom the level of hysteresis defined for the system, in order to allowthe desired negative pressure to be maintained within hysteresis limitsfor an extended period of time in which the pump does not operate.

This is achieved by the provision of a high vacuum, or negativepressure, reservoir coupled between the pump and the wound site, whereinthe high vacuum reservoir is able to store a negative pressure that isgreater, i.e. more negative, than the desired negative pressure to beapplied at the wound site. The reservoir provides a storage system forvacuum that requires periodic replenishment on a time scale that is oflonger duration than that on which the vacuum level at the wound siterequires replenishment.

The high vacuum reservoir is connected to the wound site via a vacuumregulation valve that opens when the negative pressure at the wound sitefalls to a preset minimum level and closes when an initial negativepressure at the wound site is replenished by the high vacuum reservoir.

FIG. 2 illustrates an arrangement including a high vacuum reservoir forapplying negative pressure wound therapy at a wound site 21. As for theembodiment of FIG. 1, packing material 23, such as foam, gauze or thelike, may be placed within the wound cavity, and then a drape 27 issealed to the surface of the skin around the wound site 21 forming afluid tight seal around the perimeter of the wound chamber.

A vacuum source, such as a pump, 29 is connected to a negative pressurereservoir 22 via a top-up valve 26, to allow the vacuum source 29 toevacuate the system to the desired level of vacuum. The vacuum reservoir22 is connected to the wound site 21 via reservoir valve 24 whichselectively couples the reservoir 22 to the wound site 21 to replenishthe negative pressure at the wound site. A pressure sensor 28 is coupledto the negative pressure reservoir 22 and provides a measured pressurevalue to a control unit 25. The control unit 25 is coupled to the pump29, and provides control signals to control the operation of the pump.In practice all of these elements may be contained within a singlehousing, as is traditional currently.

Optionally, the wound chamber may be connected to the reservoir valve 24via a fluid collection chamber (not shown). Such a collection chambermay include a liquid filter at an outlet thereof which will prevent flowof liquid out of the canister. In this way, the operation of thereservoir valve cannot be compromised by wound exudate containingparticulates. Alternatively, the vacuum reservoir 22 may act as a fluidcollection canister.

In operation, a wound chamber is assembled in place over the site ofapplication and connected to the vacuum source 29. The high vacuumreservoir 22, as well as the reservoir valve 24 and top-up valve 26, ispositioned between the vacuum source 29 and the wound site 21. Thevacuum pump 29 is activated and the system is evacuated to the desiredvalue for the wound site 21 (for example 80-125 mmHg below ambientatmospheric pressure). The reservoir valve 24 separating the wound site21 from the vacuum reservoir 22 closes once the desired negativepressure value is reached and the pump 29 continues to evacuate theremainder of the system. The pump 29 continues to operate until a targetlevel of negative pressure has been established in the vacuum reservoir22 (for example 200-800 mmHg below ambient atmospheric pressure).

Once the pressure measured by the pressure sensor 28 indicates that thetarget level of negative pressure has been established, the control unitdeactivates the pump 29. The control unit 25 continues to monitor thepressure in the negative pressure reservoir 22 and when the level ofnegative pressure in the vacuum reservoir 22 drops to a thresholdnegative pressure, the pump is activated and operates until the targetlevel of negative pressure has been re-established in the vacuumreservoir 22.

Thus, a high level of negative pressure is provided in the vacuumreservoir 22 which is then used to replenish the negative pressure atthe wound site 21, without requiring operation of the pump 29. The woundchamber is selectively connected to the vacuum reservoir 22 by thereservoir valve 24 in order to maintain the negative pressure at thewound site within defined limits, according to the desired level ofhysteresis. Operation of the pump 29 is only required when the level ofnegative pressure in the vacuum reservoir drops below a certainthreshold level.

The threshold negative pressure level may, for example, be equal to thedesired negative pressure at the wound site 21. Once the pressure in thevacuum reservoir 22 degrades to the desired negative pressure, it willno longer be possible for the pressure at the wound site to bereplenished to the desired level by coupling the wound chamber to thevacuum reservoir 22, and so the negative pressure in the reservoir 22must be replenished using the pump 29.

As an alternative logic could be provided in the control unit 25 suchthat if a measured pressure in the reservoir is <−2V (assuming an equalapproximate volume in the reservoir and wound chamber) then the valve 26opens on the next instance that the pressure in the wound chamber fallsto a predetermined target value, for example OV or the like.

It will be understood that the volume of and the vacuum level containedwithin the high vacuum reservoir 22 and the volume of and the vacuumlevel contained within the wound chamber formed over the wound site 21and the level of hysteresis of the reservoir valve 26 are all directlyrelated to the relative replenishment period of the high vacuumreservoir 22.

To understand the effect of the relationship between the relativevolumes of the high vacuum reservoir and the wound chamber on the periodof high vacuum reservoir replenishment, consider a system with a vacuumreservoir having equal volume to the wound chamber and running 100%hysteresis in the wound contact chamber. Let the initial vacuum in thevacuum reservoir be −5V and the vacuum in the wound contact chamber be−1V. Fluid ingress occurs and the vacuum in the wound contact chamberfalls to atmospheric pressure (0V). The connecting reservoir valve 24opens and the high vacuum reservoir 22 replenishes the wound contactchamber to −1V, leaving −4V remaining in the reservoir chamber 22.Further fluid ingress then occurs and the process repeats leaving −3V,−2V and finally −1V remaining in the vacuum reservoir 22. At this point,it will not be possible to replenish the negative pressure at the woundsite a further time to the −1 V level by coupling the wound site to thevacuum reservoir 22, and the negative pressure in the vacuum reservoir22 should be replenished. In this arrangement, the high vacuum reservoir22, of equal volume to the wound chamber, but at five-times highervacuum, extends the quiet period in between replenishment of the highvacuum reservoir by five-fold compared to the same system in the absenceof a high vacuum reservoir.

FIG. 3 shows a graph of the vacuum reservoir pressure 30 and the woundsite pressure 36 for the above described example. The pressure 30 in thenegative pressure reservoir is initially −5V and the pressure 36 at thewound site is initially −1V. The pressure at the wound site slowlydegrades due to fluid ingress and eventually falls to atmosphericpressure. At this point the reservoir valve 24 opens and the negativepressure in the vacuum reservoir 22 is used to replenish the negativepressure at the wound site. This can be seen by the drop in pressure 32in the negative pressure reservoir. This cycle repeats a further threetimes until the pressure in the negative pressure reservoir reaches −1V.When the pressure at the wound site next falls to atmospheric pressure,there is no longer sufficient negative pressure in the vacuum reservoir22 to replenish the negative pressure at the wound site, and the pump 20operates to replenish the negative pressure in the negative pressurereservoir resulting in a rise in pressure 34 in the negative pressurereservoir.

Now consider the same system with a high vacuum reservoir chamber ofdouble the volume of the wound contact chamber. In this case, the quietperiod is doubled in comparison to the above example.

Thus, the relationship between quiet periods for an arrangement as shownin FIG. 1, T_(current) of wound contact chamber volume L_(W) and initialvacuum level V_(W) and an arrangement as shown in FIG. 2 with, inaddition to the same elements, a high vacuum chamber of volume L_(HV)and initial vacuum level V_(HV), of quiet period T_(resv) is given by:T _(resv) =T _(current)(V _(HV) /V _(W))(L _(HV) /L _(W))

This relationship is true for wound contact chambers with 100%hysteresis and becomes proportionally larger in effect when lower levelsof hysteresis, H_(W)%, are specified in the wound contact chamber, asgiven by:T _(resv) =T _(current)(V _(HV) /V _(W))(L _(HV) /L _(W))(100/H _(W)%)

Thus, it can be seen that an arrangement as shown in FIG. 2 maintaininga high vacuum reservoir 22 of double the volume of the wound chamber andat double the vacuum level of the wound chamber, for a wound chamberrunning with 5% hysteresis will have a quiet period approximatelyeighty-times longer than an equivalent arrangement in line with thatshown in FIG. 1, and that this is due to the decoupling of narrowhysteresis from the running of the pump 29 utilising the high vacuumreservoir 22.

The extended quiet period can be of significant duration, depending uponthe fluid ingress levels to the system and the above parameters. Whenthe expected fluid ingress level is low, the extended quiet period maybe sufficiently long that a system in which the replenishment means canbe decoupled from the patient interface can be conceived.

When the user is about to enter a period requiring prolonged systemsilence, the high vacuum chamber can be fully charged immediately priorto this. By appropriate selection of operating parameters, it ispossible for the period of replenishment of the high vacuum reservoir 22to be sufficiently long to effectively allow the user to specify periodsof silent running of several hours immediately following replenishment.

As described above the threshold negative pressure at which the negativepressure in the vacuum reservoir must be replenished may be equal to thedesired negative pressure at the wound site. Alternatively, a higher orlower negative pressure may be selected for the threshold negativepressure.

Thus, the prolonged application of a desired negative pressure isenabled at the wound site 21. The reservoir valve connecting the vacuumreservoir 22 to the wound site 21 is fail safe and will only open whenthere is a loss of vacuum within the wound chamber. Furthermore thevalves are selected so as to close when the pressure at the wound sitereaches a desired target specified by the pressure valve manufacturer.Thus by connecting a high vacuum reservoir to a wound site via apressure regulating valve the period for which the desired negativepressure can be maintained at the wound site without operation of thepump 29 can be extended.

An example of a vacuum pressure regulation valve of a type suitableaccording to certain embodiments of the present invention is theVRD-ANB-CD vacuum regulator as supplied by Beswick Engineering™. It willbe appreciated that other fluid flow control valves used to turn on andoff a flow of fluid can be utilised according to certain embodiments ofthe present invention.

The top-up valve 26 may be of a similar type to the reservoir valve 24.Alternatively, the top-up valve may be implemented as a one-way checkvalve, or as a controllable valve under the control of the control unit25.

While example negative pressure values have been outlined above, it isenvisaged that the negative pressure range applied at the wound site forthe apparatus embodying the present invention may be between about −20mmHg and −200 mmHg (note that these pressures are relative to normalambient atmospheric pressure thus, −200 mmHg would be around 560 mmHg inpractical terms). Aptly, the pressure range may be between about −75mmHg and −150 mmHg. Alternatively a pressure range of up to −75 mmHg, upto −80 mmHg or over −80 mmHg can be used. Also aptly a pressure range ofbelow −75 mmHg could be used. Alternatively a pressure range of over−100 mmHg could be used or over −150 mmHg. Aptly the pressure of thewound chamber is between −125 mmHg and −20 mmHg. It will thus beappreciated that negative pressure is taken to mean a pressure that isless than ambient atmospheric pressure.

It will be appreciated that the various tubes are connected to the fluidreservoir via a fluid tight connection which might be either a tightfriction fit or a fitting which requires some securing mechanism such asa jubilee clip or the like. Further examples of possible methods ofconnection may be adhesive, welding or use of a snap together connectorfor example as manufactured by Colder Products.

The volume of the vacuum reservoir 22 is aptly greater than that of thewound chamber when the system is operational. More aptly, the volume ofthe vacuum reservoir is more than two-times greater than that of thewound chamber when the system is operational. Even more aptly, thevolume of the vacuum reservoir is more than four-times greater than thatof the wound interface chamber when the system is operational.

The vacuum reservoir 22 aptly does not exceed the volume of the woundchamber by more than fifty-fold when the system is operational. Moreaptly, the vacuum reservoir preferably does not exceed the volume of thewound chamber by more than twenty-fold when the system is operational.Even more aptly, the vacuum reservoir does not exceed the volume of thewound chamber by more than ten-fold when the system is operational.

If a separate fluid collection canister is present, the volume of thevacuum reservoir is aptly greater than that of the wound chamber andfluid collection canister combined when the system is operational. Moreaptly, the volume of the vacuum reservoir is more than two-times greaterthan that of the wound chamber and fluid collection canister combinedwhen the system is operational. Even more aptly, the volume of thevacuum reservoir is more than four-times greater than that of the woundchamber and fluid collection canister combined when the system isoperational.

Furthermore, in this specific embodiment, the vacuum reservoir aptlydoes not exceed the volume of the wound chamber and fluid collectioncanister combined by more than fifty-fold when the system isoperational. More aptly, the vacuum reservoir does not exceed the volumeof the wound chamber and fluid collection canister combined by more thantwenty-fold when the system is operational. Even more aptly, the vacuumreservoir does not exceed the volume of the wound chamber and fluidcollection canister combined by more than ten-fold when the system isoperational.

The vacuum reservoir 22 may be of rigid or flexible design, and if it isthe latter may contain filler of low space filling volume to maintainthe vacuum cavity.

Alternatively, a flexible vacuum reservoir may be unfilled and beallowed to collapse completely in its initial state. In this case, themechanical properties of the reservoir must be such that it can generatethe specified high vacuum when it recovers shape. Such a system mayoptionally be augmented by an internal element capable of storingmechanical energy, for example a spring of any design.

An alternative vacuum pressure regulator valve for use according tocertain embodiments of the present invention is illustrated in FIGS. 11to 18. The valve element 42 includes a channel element 48 that is formedfrom first and second resilient sidewall elements 410 a, 410 b. An inletelement 412 is inserted into a first end of the channel element 48 andholds the first and second sidewall elements 410 a, 410 b in an openspaced apart position at the first end of the channel element. An outletelement 414 is inserted into a second end of the channel element 48,holding the sidewall elements in an open spaced apart position at thesecond end of the channel element. The inlet and outlet elements have anopen cross-section, and once inserted into the channel element 48 aresealed in place. The resilient sidewall elements 410 a, 410 b are ableto move between an open configuration, in which a fluid communicationpath is provided between the sidewall elements to connect the inlet 412to the outlet 414, and a closed configuration in which inner surfaces ofthe sidewall elements are in contact, forming a seal that isolates theinlet 412 from the outlet 414.

Aptly, the first and second sidewall elements 410 a, 410 b are formedfrom a material that is able to reversibly self-seal when it comes intocontact with itself.

In use, the valve element 42 is coupled between two chambers, eachchamber containing a negative pressure (i.e. the pressure within thechambers is less than ambient atmospheric pressure). The valve element42 operates according to pressure differentials across the sidewallelements 410 a, 410 b, that is between a pressure acting on the exteriorof the sidewall elements and negative pressures acting at the inlet 412and the outlet 414. In the described example, the pressure acting on theexterior of the sidewall elements is ambient atmospheric pressure,although other pressures could be applied.

The sidewall elements 410 a, 410 b are resilient, and flex in responseto the pressure differential across them. Thus, when a negative pressureis applied to at least one of the inlet 412 and the outlet 414, thepressure differential between the atmospheric pressure acting on theexterior of the sidewall element and the negative pressure inside thechannel element 48 results in the sidewall elements being pushedtogether. If the pressure differential across the sidewall elements isof sufficient magnitude, the sidewall elements will be urged togetheruntil they come into contact isolating the inlet element 412 from theoutlet element 414.

When the sidewall elements 410 a, 410 b are in the closed configuration,the region in which the sidewall elements abut forms a zero dead-volumetube.

With the sidewall elements in the closed configuration, if the pressureinside the channel element 48 approaches ambient atmospheric pressure,the pressure differential at the sidewall elements is reduced and theresilient sidewall elements will relax into the open configuration,providing a fluid communication channel between the inlet element 412and the outlet element 414.

The pressure differential that must be applied to the valve element 42to cause the sidewall elements 410 a, 410 b to move to the closedconfiguration is determined by the device geometry, the constructionmaterials used, and the fluid enclosed within the channel element 48.

FIG. 5 shows cross-sections of the valve element 42 in a number ofoperational states. In FIG. 5(a), the valve element is coupled betweentwo chambers each containing a pressure close to ambient atmosphericpressure. No significant pressure differential is present across thesidewall elements 410 a, 410 b, and therefore the valve element 42 is inits initial open configuration. In this configuration the inlet andoutlet elements effectively hold the sidewalls apart. As the channelelement 48 is open, a fluid communication path is present through thechannel connecting the inlet 412 to the outlet 414.

FIG. 5(b) shows a cross-section of the valve element 42 when the valveelement is coupled between two chambers containing negative pressures ofsufficient magnitude to close the valve, as might be encountered if asource of negative pressure was coupled to the chamber connected to theoutlet of the valve element 42 and the system was evacuated. For thevalve element of FIG. 5(b), the pressure at the outlet 414 is lower inabsolute terms than that at the inlet 412.

In this case, the pressure differential across the sidewall elements 410a, 410 b acts to push the sidewall elements together until the innersurfaces of the sidewall elements come into contact in a central regionof the channel element 48. A temporary seal is formed in the contactregion where the sidewall elements 410 a, 410 b abut, isolating theinlet 412 from the outlet 414. This allows a higher level of negativepressure (i.e. a lower absolute pressure) to be present at the outletelement 414 than at the inlet element 412.

If fluid leaks either intentionally or unintentionally into the chamberconnected to the inlet element 412, the negative pressure at the inletelement will degrade and start to approach ambient atmospheric pressure.As the pressure at the inlet element degrades, the pressure differentialacross the sidewall elements 410 a, 410 b in a region near the inletelement will decrease. This leads to the sidewall elements 410 a, 410 bstarting to peel apart from the first end of the channel element 48. Ifthe negative pressure at the inlet 412 degrades to a threshold level,the sidewall elements 410 a, 410 b will peel apart until the sealbetween them is broken and the fluid communication path between theinlet and the outlet is restored.

FIG. 5(c) shows a cross-section of the valve element 42 at the pointwhere the sidewall elements have peeled apart from the first end of thechannel element 48 in response to the negative pressure at the inletelement degrading to the threshold level. As the sidewall elements 410a, 410 b move into the open configuration, the fluid communication pathallows negative pressure to be communicated from the outlet 414 to theinlet 412, replenishing the negative pressure in the chamber connectedto the inlet element 412 via the greater negative pressure in thechamber connected to the outlet element 414.

As the negative pressure in the chamber coupled to the inlet element 412is replenished, the pressure differential across the sidewall elements410 a, 410 b near the first end of the channel element 48 will increaseurging the sidewall elements together and throttling the communicationof negative pressure between the inlet and outlet elements.

The threshold pressure at the inlet element 412, at which the valveopens and closes can be controlled by selection of the device geometry,construction materials and the enclosed fluid within the valve element42.

FIG. 6 shows a graph illustrating pressure against time for an examplescenario in which two chambers, each of 50 ml in volume, are coupled viathe valve element 2. Initially, a first chamber coupled to the inletelement 12 was evacuated to a negative pressure of approximately −65mmHg (i.e. 700 mmHg absolute), and a second chamber coupled to theoutlet element 14 was evacuated to a negative pressure of approximately−585 mmHg (i.e. 180 mmHg absolute). A leak of 50 ml/h was introducedinto the first chamber, and the negative pressure level in both chamberswas recorded for approximately an hour. Initially, the valve elementwill be in a configuration similar to that shown in FIG. 5(b).

In an initial stage (i) the pressure in the first chamber is seen tosteadily decrease, and the pressure in the second chamber is maintainedat a constant level. As the negative pressure in the first chamberdecreases, the pressure differential across the sidewall elements at thefirst end of the channel element decreases and the sidewall elementsbegin to peel apart. When the negative pressure in the first chamberreaches the threshold value, the valve element 42 begins to open as canbe seen in stage (ii).

In stage (ii), the negative pressure level in the second chamber can beseen to decrease, as negative pressure is communicated from the secondchamber to the first chamber to compensate for the leak. The level ofnegative pressure in the first chamber can be seen to degrade at aslower rate as the valve element 42 opens, and then steadily thenegative pressure in the first chamber is replenished.

Eventually, the negative pressure in the second chamber degrades to thelevel of the negative pressure in the first chamber, as can be seen instage (iii). At this point, the valve element 42 is fully open and thenegative pressure in the first and second chambers is equalized. Thenegative pressure in both chambers then continues to degrade at the leakrate.

The valve element 42 can be used in any application requiring aspecified level of vacuum to be transmitted to and or maintained in asystem. For example, some medical applications require the applicationof negative pressure to a bodily location. The level of vacuum suppliedby a vacuum pump (in situ or via a wall-line) may be excessive for thechosen application. By coupling the valve element 42 between the vacuumsource and the site of application, the level of negative pressureapplied can be regulated to not exceed the level specified by thethreshold negative pressure of the valve element 42. One example medicalapplication is the provision of negative pressure at a wound site intopical negative pressure therapy.

FIG. 10 shows an example arrangement including the valve element 42 forapplying topical negative pressure to a wound site 430. A packingmaterial 432, such as foam, gauze or the like, is placed within a woundcavity, and then a drape 434 is sealed to the surface of the skin aroundthe wound site 430 forming a fluid tight seal around the perimeter of awound chamber. A source of negative pressure 438, such as a negativepressure reservoir, is coupled to the wound cavity via the valve element42 and a tube 436. Optionally, a fluid collection canister (not shown)may be coupled between the valve 42 and the wound chamber to collect anywound exudate drawn from the wound site 430. The use of the packingmaterial 432 is optional, and it may be omitted in certain arrangementsas appropriate.

The negative pressure reservoir 438 may be connectable to a poweredsource of negative pressure operable to evacuate the system down toinitial negative pressure levels.

Whilst embodiments of the present invention will be describedhereinafter by way of reference to a wound chamber defined at a woundsite under a drape it will be understood that certain embodiments of thepresent invention can be utilised to maintain a negative pressure in awound chamber which is a rigid structure or partly rigid structure suchas a cup device placed over a wound site.

Initially, the wound site and the negative pressure reservoir 38 are atambient atmospheric pressure. A powered source of negative pressure isthen coupled to the negative pressure reservoir 438 and operates toevacuate the system. As the pressure at the inlet and outlet elements isinitially at ambient atmospheric pressure, the valve element 42 will bein its initial open state, as shown in FIG. 5(a). Thus, negativepressure generated in the negative pressure reservoir 438 will becommunicated through the open valve element 42 to the wound site 430.

Once the negative pressure at the wound site, and therefore at the inletelement 412, reaches a threshold level the pressure differential actingon the sidewall elements 410 a, 410 b will urge the sidewall elementstogether, closing the valve element 42, as shown in FIG. 5(b). Thepowered source of negative pressure can then continue to evacuate thenegative pressure reservoir, isolated from the wound site 430 by thevalve element 42. Thus, the negative pressure established in thenegative pressure reservoir 438 may be higher, that is more negative,than that experienced at the wound site 430. Once the desired level ofnegative pressure is established in the negative pressure reservoir 438,the powered source of negative pressure can be disabled or removed fromthe system.

Over time, small leakage paths will form that allow fluid to leak intothe wound chamber. Ingress of fluid such as wound exudate or gas intothe wound chamber will lead to the negative pressure at the wound siteslowly degrading, i.e. the pressure becoming less negative. Once thenegative pressure at the wound site 430 degrades to a certain level, thevalve element 42 will begin to open, as shown in FIG. 5(c), allowingnegative pressure to be communicated from the negative pressurereservoir 438 to the wound site 430 to replenish the negative pressureat the wound site. The negative pressures at the wound site and in thenegative pressure reservoir will follow a profile similar to that shownin FIG. 6.

Thus, the valve element 42 is able to automatically control thecommunication of negative pressure from the negative pressure reservoir438 to the wound site 430 in order to maintain the negative pressureapplied to the wound site within certain limits. Once the negativepressure in the negative pressure reservoir 438 equalizes with thenegative pressure at the wound site, the powered source of negativepressure may be used to re-establish the initial level of negativepressure in the negative pressure reservoir.

The volume of the vacuum reservoir 438 is preferably greater than thatof the wound chamber when the system is operational. This extends thetime period for which the negative pressure reservoir 438 is able tomaintain the negative pressure at the wound site 430 within the desiredlimits.

Alternatively, the negative pressure reservoir 438 may be omitted andthe valve element 42 may be coupled between the wound site 430 and apowered source of negative pressure such as a pump, or an externalvacuum line. The negative pressure provided by the pump or the vacuumline may be too great in value to be applied directly to the wound site.However, by coupling the valve element 42 between the source of negativepressure and the wound site, the negative pressure applied at the woundsite 430 will be regulated according to the threshold negative pressurevalue of the valve element 42.

It is envisaged that the negative pressure range applied at the woundsite for the apparatus embodying the present invention may be betweenabout −20 mmHg and −200 mmHg (note that these pressures are relative tonormal ambient atmospheric pressure thus, −200 mmHg would be around 560mmHg in practical terms). Aptly, the pressure range may be between about−75 mmHg and −150 mmHg. Alternatively a pressure range of up to −75mmHg, up to −80 mmHg or over −80 mmHg can be used. Also aptly a pressurerange of below −75 mmHg could be used. Alternatively a pressure range ofover −100 mmHg could be used or over −150 mmHg. Aptly the pressure ofthe wound chamber is between −125 mmHg and −20 mmHg. It will thus beappreciated that negative pressure is taken to mean a pressure that isless than ambient atmospheric pressure.

It will be appreciated that the various tubes are connected via a fluidtight connection which might be either a tight friction fit or a fittingwhich requires some securing mechanism such as a jubilee clip or thelike. Further examples of possible methods of connection may beadhesive, welding or use of a snap together connector for example asmanufactured by Colder Products.

FIG. 7 illustrates an exemplary method of fabricating the channelelement 8 for manufacturing the valve element 2. According to theillustrated method, in a first step of the method a first flat sheet 410of elastomeric material is cast, for example a 2 mm thick sheet of 300mm by 300 mm formed of a two-part heat-curable silicone elastomer (forexample Wacker Chemie AG), or a polyurethane elastomer. Masking strips412, for example strips of acetate sheet having a width of 10 mm and athickness of 50 μm, are laid upon the first flat sheet 410 allowingsufficient spacing to separate individual channel elements whencomplete. A second flat sheet 414 of elastomeric material is then curedin situ on top of the first sheet 410, sandwiching the acetate strips inplace. The individual flat tubes, forming the channel elements, are thenseparated from each other and cut to a desired length (for example 40mm). The acetate strips 412 can then be removed from each of the flattubes, resulting in reversibly self-sealing channel elements 8comprising tubes of zero dead-volume.

It will be understood that the term dead-volume relates to the volumeenclosed within the channel element 48 when the tube is in its initialclosed position. In the above described channel elements 48, thesidewall elements abut along the length of the channel once the acetatestrips 4412 have been removed. Thus, there is no volume enclosed betweenthe sidewall elements 48, resulting in a zero dead-volume tube. Incontrast, attempting to flatten a tube of cylindrical cross-sectionwould inevitably lead to pinched regions at the edges of the flattenedtube having some dead-volume through which fluid could continue to flow.

In order to form the valve element 42, the inlet element 412 and outletelement 414 are inserted into opposite ends of the channel element 48,as illustrated in FIG. 8. The inlet and outlet elements are of opencross-section, for example tubing of open aspect having an internaldiameter of 4 mm and an external diameter of 8 mm. The inlet and outletelements hold apart the sidewall elements 410 a, 410 b of the channelelement 48 at the respective ends of the channel element.

The threshold operating pressure of the valve element 42 can beconfigured by setting the end-to-end separation of the inlet and outletelements, that is the distance between the ends of the inlet and outletelements inserted into the channel. The end-to-end separation requiredto configure a certain threshold operating pressure depends on thematerials used in the construction of the valve element, and thedimensions of the channel element. In the example illustrated in FIG. 6,an end-to-end separation of 10 mm was used.

FIG. 9 shows cross-sections of valve elements with no pressuredifferential applied to the sidewalls and having different end-to-endseparations 411 of the inlet and outlet elements 412, 414. For the valveelement illustrated in FIG. 9(a), the end-to-end separation 411 is tooshort, meaning that the valve will not close as desired or will have avery high threshold negative pressure (i.e. very low absolute thresholdpressure). Conversely, if the end-to-end separation 411 is too large asshown in FIG. 9(c), the valve element may be initially closed when nopressure differential is applied. The valve element 42 shown in FIG.9(c) will therefore be unable to regulate a negative pressure; howeversuch a valve element may be operable to selectively provide a fluidcommunication path if a positive pressure (greater than ambientatmospheric pressure) is applied to the inlet and outlet elements.

FIG. 9(b) illustrates a cross-section of a valve element 42 having anend-to-end separation 411 of the inlet and outlet elements such that thevalve element will be operable to regulate the communication of negativepressure.

For a valve element fabricated according to the method described inrelation to FIGS. 7 and 8, it has been found that a valve element withan end-to-end separation 11 of 3 mm did not shut (DNS) when an absolutepressure of 180 mmHg was established at both the inlet and the outlet.Conversely, a valve element having an end-to-end separation of 15 mm ormore was permanently closed even when no pressure differential waspresent across the sidewall elements. In between these extremes, it wasfound that the threshold operating pressure (absolute) of the valveelement increases with increasing end-to-end separation, and thereforethe negative pressure level required for closure decreases withincreasing end-to-end separation 411.

Table 1 shows experimental results for the pressure at the inlet 412 atclosure for valve elements fabricated according to the above describedmethod having end-to-end separations 11 of 3 mm, 7 mm, 10 mm, and 12 mm.The valve elements where coupled between two chambers at ambientatmospheric pressure, and then the system was evacuated down to 180 mmHgabsolute pressure via a pump connected to the chamber coupled to theoutlet 414. The pressure at which the valve element closed was recorded.This procedure was repeated ten times for each valve element, and theresults are recorded in Table 1. Pressures values in Table 1 areabsolute pressures in units of mmHg.

TABLE 1 3 mm 7 mm 10 mm 12 mm DNS 507 715 716 DNS 525 722 732 DNS 519721 732 DNS 519 719 732 DNS 513 722 734 DNS 516 720 734 DNS 514 717 730DNS 517 718 735 DNS 513 716 731 DNS 524 719 732

As can be seen from Table 1, the threshold pressure for the valveelement 42 is strongly dependent on end-to-end separation 411 of theinlet 412 and outlet 414 elements, allowing the valve element to beconstructed for a desired threshold pressure by controlling theend-to-end separation.

As will be understood, for a valve element made from differentmaterials, or having different sidewall thicknesses, the end-to-endseparation 411 required for a particular threshold pressure will varyfrom the examples given above.

As the channel element 48 is constructed as a zero dead-volume tube, theregion in which the sidewall elements 410 a, 410 b abut when in theclosed configuration will form a zero dead-volume seal, that is therewill be no volume in which fluid may be trapped between the sidewallelements within the region of the channel element where the sidewallelements abut.

Another example of a pressure regulator valve is thermo formable plastictube which is heat deformed by making contact with a heated elementunder controlled temperature pressure and time resulting in a tube thatcollapses with certain internal reduced pressure or vacuum compared tothe external pressure.

It would be known to the skilled person that any plastic that could bedeformed by a heat treatment could be suitable as the material for thethermo formable plastic tube of the present invention. There may be oneor more heating elements to produce the deformed channel or tube. It ispossible that one heat element could be used in the heat and pressureprocess to produce a deformed channel or tube. It is even foreseen thatone heat element could be used and the channel or tube or rotated todeform the channel or tube in various places to give the final deformedchannel or tube. The heat and pressure process may be repeated, usingthe same heat and pressure measurements or different temperature,pressure and durations as required to give the final deformed channel ortube. In a preferred heat and pressure process two or more opposingheating elements would be used in a single compressing action on thetube.

Preferably the thermo formable plastic is a thermoplastic elastomer(TPE), thermoplastic elastomers are well known in the art and theirproperties are well known.

Suitable thermoplastic elastomers (TPE) (thermos formable elastomers)include but are not limited to, all six generic classes of TPEs, whichare Styrenic block copolymers, polyolefin blends, elastomeric alloys(TPE-v or TPV), thermoplastic polyurethanes, thermoplastic copolyesterand thermoplastic polymides. Examples of TPE products that come fromblock copolymers group are Arnitel (DSM), Engage (Dow chemical), Hytrel(Du Pont), Kraton (Shell chemicals), Pebax (Arkema), Pellethane,Riteflex (Ticona), Styroflex (BASF) and more. While there are now manycommercial products of elastomer alloy, these include: Alcryn (Du Pont),Dryflex, Evoprene (AlphaGary), Forprene, Geolast (Monsanta), Mediprene,Santoprene and Sarlink (DSM).

Any suitable width of a heating element for deforming the tube could beused depending on the required properties of the tube, for example thereduced pressure in which cause collapse and closure of the tube.

Typical width of a suitable heating element may be 2 to 15 mm, 3 to 13mm, 5 to 12 mm or any other suitable width.

The suitable width of the heating element may be dependent on the typeof tube and its properties e.g. diameter, wall thickness, materialconstruction.

For a tubing of Outer Diameter (OD) 12 mm a suitable width of heatingelement may be 2 to 20 mm.

The temperature used to deform the tube can be any suitable temperatureto deform the tube and may depend on the properties of the tubediameter, wall thickness, material and construction.

Typically this maybe 80 to 180° Celsius (C), 80 to 165° C., 90 to 110°C., 93 to 107° C., 95 to 105° C., 97 to 101° C., 98 to 100° C. etc.

The deformation time may also be dependent on the properties of the tubeand heat element process and can be any suitable duration required todeform the tube to the desired properties. This could be a matter of afew seconds or more e.g. 3 seconds.

After deformation by heat as explained above, the tube may require asetting or cooling period to maintain the geometry or properties of thedeformation.

This again will depend on the starting materials, tube, heat element,pressure, time of deformation etc.

The setting or cooler period could be for example 80° C. for 10 minutes.

It is foreseen that the deformation and setting period could be afunction of time and temperature.

Also, the heat deformation process may have the heated elements pinchedfor the required heating time and then released, with the cooling periodtaking place without the heating element in contact with the tube.

Or in other embodiments the heating element may remain in contact withthe tube during the cooling/setting period.

The cooling/setting period may not be time dependent but depending onreaching a target temperature e.g. from around 100° C. at the heatelement process to a final setting/coolant temperature of e.g. 80° C.

The heated deforming element/bar may be any suitable shape or geometryfor example flat, curved including semicircular, and in flat with radiusedges.

It is foreseen that in the heat deforming process that there are twoheated forming bars in which between these heated deforming bars theplastic tube/TPE tube is placed prior to the heat deforming process.

It is foreseen that the heated bars clamp or compress the plastic/TPEtube deforming the tube.

The two bars may fully compress the tube according to an appliedpressure (as illustrated in FIG. 12) and or may compress the tube to adesired separation/distance as illustrated in FIG. 13.

FIG. 11 illustrates a tube or channel element 51 with two opposing sidewalls 52 and 53, defining a channel 54. The tube is placed in-betweentwo heating elements 55 and 56. FIG. 11 shows the channel open, andbefore a heat and pressure process.

FIG. 12 illustrates that the heating elements 55 and 56 have pinched thetube 51 creating on the two opposing side walls 52 and 52 a substantialflat portion where the heating elements 55 and 56 compressed the tube51. FIG. 12 illustrates the heat and compression process.

FIG. 13 illustrates and alternative embodiment of the heat andcompression process where the heating elements 55 and 56 are preventedfrom coming into contact with each other by stops 57 and thus the tube51 is not completely crushed. The size of the stops 57 may varyaccording to the size of the tube 51 and the desire compression requiredin the heat and compression process.

According to the invention there is provided a method of manufacturer ofa channel element for selectively providing a fluid communication path,the method comprising:

subjecting a channel element to a deformation process in which theopposing sidewalls of the channel element are deformed to aid movementbetween an open configuration when the opposing side walls are apart anda closed configuration when the opposing side walls abut, to close oropen the channel of the channel element, responsive to a pressuredifference at or on the side walls between the inside surface and theoutside surface of the opposing walls.

According to the invention there is provided a channel element forselectively providing a fluid communication path, comprising:

a deformed channel in which the opposing sidewalls of the channelelement are deformed to aid movement between an open configuration whenthe opposing side walls are apart and a closed configuration when theopposing side walls abut, to close or open the channel of the channelelement, responsive to a pressure difference at or on the side wallsbetween the inside surface and the outside surface of the opposingwalls.

The channel element may be a tube. This tube may be circular, oval,square, rectangle, elliptical or any other suitable shape. The tube maybe cross sectioned. The channel element may be irreversibly deformed bythe process. The channel element or tube mat be deformed by a heat andpressure process that deforms the channel element or tube whether thisis irreversibly deformed or not.

The valves according to the present invention can be used in manysituations. The valves may be used with further integral tubing orchannels, or be used where further tubing or channels are attached atone or more ends of the valve to allow fluid communication between twopoints. In the cases where integral tubing is inserted into the ends,this tubing may be optionally be used to hold the side wall elementsapart in a manner similar to the previous flat valve embodimentdescribed herein.

It is foreseen that the present invention could be used in a negativepressure treatment system similar to but not limited to that describedin FIG. 2, with a wound dressing, pump to create the negative pressure,possibly a canister to collect the wound exudate although in alternativesystems, the dressing is able to do this function without the need for acanister for example by employing a superabsorber material in thedressing.

The dressing could be various dressings known in the art and used forsuch purposes. Typically the dressing will have a cover and wound spacermaterial or a material to collect the exudate. The negative pressuretreatment system would usually have various tubes and valves allowingfluid communication between the various components in order for thesystem to work. For example a channel or tube from the wound area to thecanister and then to the pump.

The dressing may have a seal to aid sealing of the dressing to the skinof the patient. The sealant may be any known in the art and couldinclude but not limited to silicon adhesives and or acrylics. Specificexamples could include but again not be limited to are Duoderm fromConvTec and Replicare from Coloplast.

Example 1 Preparation of a Vacuum Valve by Partially Sealing ContinuousTubing

Thermoplastic elastomeric (TPE) tubing (Cole-Parmer, Clear C-Flextubing, item WZ-06422-15) of ½″ OD (12 mm) and ⅜″ (9 mm) ID, asillustrated in FIG. 14 was heat sealed with a 9 mm wide heating elementin a direction perpendicular to its long axis, as illustrated in FIG. 15at a temperature of 98-100° C. for a welding time of 3.0 seconds, at 3Bars pressure (300 kilo-Pascals) and cooled to 80° C. prior to sealerjaws releasing the sample.

The result was a partially deformed tube, deformed at the sides of thetube (the area receiving maximum pressure) but remaining unsealed acrossits centre, as illustrated in FIGS. 16, 17 and 18.

The tubing was trimmed in a direction perpendicular to the long axis ofthe tube at a distance of 40 mm from the weld.

Example 2 Performance of a Vacuum Valve by Partially Sealing ContinuousTubing

The valve prepared in Example 1 was fitted to a source of vacuum andvacuum gauges were placed between the source of vacuum and the valve andon the side of the valve distal to the vacuum source. The vacuum sourcewas turned on and generated a vacuum of 202 mmHg on the proximal side ofthe valve while the vacuum was 557 mmHg on the distal side of the valve,thus demonstrating the operation of the valve. The ambient pressure was756 mmHg, thus the valve closed at a vacuum of 200 mmHg below ambientatmospheric pressure.

Example 3 Of a Vacuum Regulation Valve Prepared by Heat-Sealing aThermoplastic Elastomeric Tube

Transparent thermoplastic elastomer tubing (Clear C-flex tubing, ⅜″ ID(9 mm), ½″ (12 mm) OD, Cole-Parmer Instrument Company Ltd) was cut to a100 mm length and heat-sealed in a direction perpendicular to itslongest axis at its mid-point. The heat sealer used was a Hulme MartinHM1000P Portable heat sealer with a 3 mm band run on heat setting 10 andcooling setting 10, 315 W per seal. Only one of the jaws of this heatsealer is heated and so the tube was rotated along its long axis by halfa turn and the procedure repeated. This process was repeated 3-times ineach orientation. Following this, the same process was repeated, 2-timesin each orientation, on both adjacent sides of the central 3 mm wideband, resulting in a heat-sealed section approximately 10 mm in width.This process did not seal the tube but generated crimped internal foldsthat enabled the tube to fully seal across its width when containing avacuum. The valve described above had a closing pressure of 200 mmHgbelow ambient atmospheric pressure.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, means “including but not limited to”, andis not intended to (and does not) exclude other moieties, additives,components, integers or steps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith.

What is claimed is:
 1. Apparatus for providing negative pressure at awound site, the apparatus comprising: a negative pressure reservoirconfigured to contain a first zone of negative pressure; a chamberconfigured to contain a second zone of negative pressure, the chamberconfigured to communicate negative pressure to a wound dressing; and avalve element arranged to selectively provide a fluid communication pathbetween the reservoir and the chamber, the valve element comprising anexterior surface exposed to an ambient atmospheric pressure, an innersurface fixed relative to the exterior surface such that movement of theexterior surface causes movement of the inner surface, a first portionof the inner surface configured to be exposed to the first zone ofnegative pressure, and a second portion of the inner surface configuredto be exposed to the second zone of negative pressure, the valve elementfurther arranged to selectively block the fluid communication path whenthe exterior surface moves to a first position, the valve elementfurther arranged to selectively open the fluid communication path whenthe exterior surface moves to a second position, wherein the exteriorsurface moves from the first position to the second position as a resultof the ambient atmospheric pressure acting on the exterior surface and anegative pressure acting on the inner surface.
 2. The apparatus of claim1, further comprising: a suction pump for generating negative pressure,wherein in response to a pressure in the negative pressure reservoirdecreasing to a threshold negative pressure, the suction pump isoperable to re-establish an initial negative pressure in the negativepressure reservoir; and a further valve element coupled between thenegative pressure reservoir and the suction pump, the further valveelement configured to connect the suction pump to the negative pressurereservoir when the pressure in the negative pressure reservoir decreasesto the threshold negative pressure.
 3. The apparatus of claim 2, furthercomprising a pressure sensor arranged to monitor the negative pressurein the negative pressure reservoir.
 4. The apparatus as claimed in claim3, further comprising a controller configured to control the suctionpump to provide the initial negative pressure in the negative pressurereservoir in dependence of a pressure at the pressure sensor.
 5. Theapparatus of claim 2, wherein the initial negative pressure comprises anegative pressure of greater than 200 mmHg below atmospheric pressure.6. The apparatus as claimed in claim 5, wherein the initial negativepressure comprises a negative pressure of greater than 500 mmHg belowatmospheric pressure.
 7. The apparatus of claim 1, wherein the negativepressure reservoir comprises a fluid collection chamber for collectingwound exudate drawn from the wound site.
 8. The apparatus of claim 1,further comprising the wound dressing configured to be disposed over thewound site.
 9. The apparatus of claim 1, wherein the negative pressurereservoir comprises a vacuum chamber having a volume more than double avolume of a wound chamber defining a space between a wound surface andan impermeable wound cover when a desired negative pressure is appliedto the wound chamber.
 10. The apparatus of claim 9, wherein said desirednegative pressure at the wound site comprises less than around 200 mmHgbelow atmospheric pressure.
 11. A method of providing negative pressureat a wound site, the method comprising: while a negative pressure in anegative pressure reservoir is greater than a threshold negativepressure, selectively providing a fluid communication path between thenegative pressure reservoir and the wound site via a valve element toprovide a desired negative pressure at the wound site, the valve elementcomprising an exterior surface exposed to an ambient atmosphericpressure, an inner surface fixed relative to the exterior surface suchthat movement of the exterior surface causes movement of the innersurface, a first portion of the inner surface configured to be exposedto a first zone of negative pressure contained within the negativepressure reservoir, and a second portion of the inner surface configuredto be exposed to a second zone of negative pressure under a wounddressing placed over at least a portion of the wound site, the valveelement further arranged to selectively block the fluid communicationpath when the exterior surface moves to a first position, the valveelement further arranged to selectively open the fluid communicationpath when the exterior surface moves to a second position, wherein theexterior surface moves from the first position to the second position asa result of the ambient atmospheric pressure acting on the exteriorsurface and a negative pressure acting on the inner surface; and inresponse to the negative pressure in the negative pressure reservoirdecreasing to the threshold negative pressure, re-establishing initialnegative pressure in the negative pressure reservoir via a suction pump.12. The method as claimed in claim 11, wherein operating the suctionpump further comprises providing a negative pressure in the negativepressure reservoir of greater than 250 mmHg below atmospheric pressure.13. The method as claimed in claim 12, wherein operating the suctionpump further comprises providing a negative pressure in the negativepressure reservoir of greater than 500 mmHg below atmospheric pressure.14. The method as claimed in claim 11, further comprising monitoring thenegative pressure in the negative pressure reservoir via a pressuresensor, wherein operating the suction pump comprises operating thesuction pump in response to a pressure monitored at the pressure sensor.15. The method as claimed in claim 11, wherein the threshold pressure isequal to the desired negative pressure at the wound site.
 16. Theapparatus of claim 1, in which the valve element arranged to selectivelyprovide the fluid communication path between the reservoir and thechamber comprises: a channel element having opposed sidewall elementslocatable in an open spaced apart configuration in which a channel isprovided between the sidewall elements and in a closed configuration inwhich the sidewall elements abut to close the channel; wherein thesidewall elements are resilient and are moveable to said openconfiguration in which the channel provides a fluid communication pathor said closed configuration responsive to a pressure difference at oron the sidewall elements.
 17. Apparatus for selectively providing afluid communication path comprising: a channel element comprisingopposed sidewall elements locatable in an open spaced apartconfiguration in which a channel is provided between the sidewallelements and in a closed configuration in which the sidewall elementsabut to close the channel, each of the sidewall elements comprising anouter surface exposed to an atmospheric pressure and an inner surfaceexposed to a first negative pressure under a wound dressing, the innersurface being spaced apart from and fixed relative to the outer surface;wherein the sidewall elements are resilient and are moveable to saidopen configuration in which the channel provides a fluid communicationpath or said closed configuration responsive to a pressure differencebetween the outer and inner surfaces of the sidewall elements.
 18. Theapparatus as claimed in claim 17, wherein the pressure differencecomprises a difference between a pressure on the outer surface of atleast one sidewall element of the channel element and a pressure on aninner surface of at least one sidewall element.
 19. The apparatus asclaimed in claim 18, wherein the pressure difference comprises adifference between atmospheric pressure and a pressure less thanatmospheric pressure.
 20. The apparatus as claimed in claim 17, whereinthe sidewall elements are urged together into the closed configurationwhen the pressure difference is greater than a threshold pressuredifference.
 21. The apparatus as claimed in claim 17, furthercomprising: an inlet element arranged to hold the sidewall elements inan open spaced apart configuration at a first end region of the channelelement; and an outlet element arranged to hold the sidewall elements inan open spaced apart configuration at a further end region of thechannel element.
 22. The apparatus as claimed in claim 16, furthercomprising a rigid housing surrounding at least a portion of the channelelement.
 23. The apparatus as claimed in claim 16, wherein the sidewallelements are formed from a material that reversibly self-seals when itcomes into contact with itself.
 24. The apparatus as claimed in claim23, wherein the sidewall elements are formed form a silicone elastomeror a polyurethane elastomer.